Composition of matter for platinum surstitute in electrical terminals and other uses



F. A. FAHRENWALD.

COMPOSITION 0F MATTER FOR PLATINUM SUBSTITUTE IN ELECTRICAL TERMINALSAND OTHER USES.

APPLICATION FILED FEB. I8, 1918.

1,339,505. Patented May 11, 1920.

fly-5 winrar UNITED sTATEs PATENT oEEIcE.

TRANI: A. EAHEENWALD, 0E CLEVELAND, omo, AssI'GNoE To TIIE EIIOTANIUMCCIEPANY, or CLEVELAND, omo, A CoEPoEATIoN oF oIIIo. y

AND OTHER UsEs.

d www of Letters ment. Patented May 11, 1920. Original applications No.108,991, lcd' July 13, 1916, and No. 129,911, filed November 6,1918.Divided and this application illed February 18,1919 vSerial No. 217,885.i .i

To all whom it may concern.'

Be it known that I, FnANx A. FAIIEEN- WAL'D, a citizen of the UnitedStates, residing at Cleveland, in the county of Cuyahoga and State ofOhio, have invented a certain new and useful Improvement in Compositionof Matter for latinum Substitute in Electrical Terminals and other Uses,of which the followin is a full, clear, and ex` act description, reerence being had to the accompanying drawings.

This invention relates to an improvement in alloys and has for itsobject to provide a composition of metal which may be employed in manycases as a substitute formetallic platinum and expensive platinum alloysin various types of electrical construction, as spark devices,resistance elements, thermo-couple elements, etc., and in articles ofjewelry, chemical containers, and the like, as well as in dentistryphilosophical instruments and surgery. 'lhe qualities of platinum whichrender it of such great use in these fields have been Iits hardness(especially when alloyed with iridium), its high melting point (which isalso heightened y alloying with iridium or the like), and its resistanceto oxidation and chemical action, which prevents it from erosion byelectrical influences or from corrosion by acids or oxidizinginfluences.

The objects of my invention are the provision of an alloy material whichshall be substantially'equal to platinum in respect of hardness, meltingpoint, and electrical and chemical resistivlty so as to be usable forspark points, electrical terminals, resistance elements, electrochemical apparatus, chemical containers, and other uses where it isexposed t0 severe corrosive conditions. Another obj ect is the provisionof an alloy havin the above characteristics and also sufficientlymalleable, ductile, and homogeneous to permit ofl rolling, drawing,stamping or otherwise working to the desired shape; the provision of analloy of such homogeneous character as not to be hot short or subject toselective corrosion; the provision of an alloy which shall not onlyconserve the worlds supply of platinum but shall be less expensive thanplatinum; while other objects and advantages will appear as the description proceeds; this application being a vision of my two earlierapplications Nos.

vIn view of the 108,991 and 129,911 sled July 13, 191e and November 6,1916, respectively.

The exacting Inature of the uses in view immediately exclude fromconsideration all metals of a readily fusible or oxidizable nature; and`alloys of the solid solution type are always preferable to other alloysas bemg more ductible, malleable, homogeneous alld chemically resistantthan other types of a oys.

I have discovered that the alloys of gold and palladium, if made of theproper percentage composition, and of the proper degree of purity, (orif certain improper impurities are avoided), will make a complete seriesof solid solutions of remarkable malleability, ductility andhomogeneity; of a hardness fully comparable with that of platinum, amelting point sufliciently high for all practical purposes for whichplatinum is generally used, an electrical resistivity fully equal `tothat of platinum, and a chemical resistivity even more pronounced thanthat of platinum. fact that a substitute for platinum is the object ofthis invention platinum itself should not be included to more than asmall percentage, although in small quantities it is not injurious.Likewise the metals rhodium, ruthenium and iridium are too rare andcostly to be used in large amounts, although they are not deleterious.In fact commercial palladium contains on the average about one half ofone per cent. of platinum as' an impurity and, requently other noblemetals as iridium or rhodium also; itis very rarely free from thesesubstances, especially platinum, and I have known commercial palladiumto contain as much as ive per cent. of platinum. The cost of refiningbeing greater than the value of the noble metal impurities, I have nevertaken the precaution of purifying the palladium, and consequently myinvention is t0 be considered as independent of the presence or absenceof these substances tol a small percentage, whether intentionally orinadvertently present. against the presence of base metals, such asiron, cobalt, nickel, copper, lead and other oxidizable substances.

In the drawings accompanying and forming a part of this application,Figure 1 rep- It is necessary, however, to guard coMrosITIoN CE MATTEREon. PLATINUM suns'rITUTE` vIN ELECTRICAL TEEMINALS resents the meltingpoint and hardness curves of the gold-palladium series; Fig. 2illustrates the melting points and hardness value of pure gold, silver,platinum and alladium upon the same scale; Fig. 3 il ustrates theconductivity (both thermal and electrical) of the gold-palladiumseries;-Fi 4 illustrates the conductivities of pure gol silver, platinumand palladium upon the same scale; Fig. 5 represents a photomicrographsection showing .the se egation of palladium from achilled solutlon ingold;

ig. 6 represents a photomicrograph section of the same alloy magnifiedmuch more strongly; Fig. 7 represents the condition of the same alloyupon slow cooling; Fig. 8 illustrates a pair of spark points constructedfrom my im roved gold-palladium alloy; and Fi 9 i ustratesa chemicalutensil of the sai improved material.

The range of temperature through which partial fusion occurs in an alloyof gold and palladium is very small both ascending and descending, andthe melting point increases rapidly with the first increment ofpalladium, so that a decided advantage is afforded by the addition ofsmall proportions of this substance, out of all ratio to its cost. Itwill also be seen from Fig. 1 that the hardness of the alloy is greaterin each case than the hardness-of either constituent, being at a maximumsubstantially at the time that the two metals are present in equalatomic proportions, which is equivalent approximately to palladium 40,gold 60 by wei ht. A hardness equal to that of platinum 1s obtained withonly twenty per cent. of palladium, while the maximum hardness is abouttwenty per cent. greater than that of pure platinum. Reference to Fig. 3shows that the conductivity of the alloy is much less than theconductivity of either of the component metals, the curve showin a verydecided slope at each end, indicatlng a sudden increase of resistancecaused by the admixvture of a small amount of the other metal, theconductivity also, as will be expected, reaching a minimum under thecondition of equal atomic proportions. In fact an alloy of goldeighty-five per cent. palladium fifteen per cent. (atomic) has the sameresistance as pure platinum, while an increase in the palladium contentlowers the conductivity only to one third that of platinum; this,coupled with the chemical resistivity of the alloy and its resistance tofusion or oxidation at high temperatures, indicates clearly its value asan electrical resistance wire, for spark points it can be made wide andlow to offset this as shownl in Fig. 8. In fact the 20 per cent. alloywhich is the one most frequently used, is not appreciably inferior toplatinum in this regard.

gation upon cooling is very small, but -experience proves that if amolten solution of .the two substances containing more than about tenatomic per cent. of palladium is l suddenly chilled, a sli htlysegregated condition 1s secured suc as represented in exa geratedfashion in Fi.` 5 and in a more hig ly magnified way in ig. 6, the'center of each metallic crystal being peculiarly rich in palladium andthe margins of the crystals grading off to a lower composition. An artice so constituted possesses a resistivity to heat, electrical abrasionand chemical action equivalent only to the lowest alloy which itcontains; but by cooling the same alloy slowly or by maintaining thealloy fora considerable eriod at a temperature near but not above itsmelting point, a re-arrangement of each crystal can be secured andperfect homogeneity obtained as shown in Fig. 7.

For many uses in s ark points, electrical contact terminals, philosohical ap aratus and dentistry, an alloy ofp old andp palladium in theproportions o palladium 10 per cent. gold 90 per cent. (atomic) will besuflicient, (equivalent to Pd. 5.6, Au. 94.4 by weight) since such analloy will have a melting point 100 C. higher than that of pure gold anda hardness substantially midway between that of gold and platinum. f

Such an alloy, however, is hardly sufiiciently resistant physically foruse in crucibles and like chemical apparatus, owing to its softness andthe dan er of accidental melting, although it is o great value in dentalfoil, its hardness being suiiciently small to permit manipulation, andits melting point being sufliciently high to permit the melting of goldthereon if performed with reasonable care.

For the majority of uses, both electrical and chemical, I recommend analloy containing approximately gold 80 per cent. atomic),palladium 20per cent. (atomic) equivalent approximately to Au. 88, Pd.

2, by weight), since such an alloy will have a melting pointapproximatel 1250o C. which is sufficiently high to avoi an danger ofbeing melted accidentally un er ordinary conditions of use. Such analloy has a hardness substantiall equal to that of platinum,l and is osuch resistance to chemical, electrical and atmospheric corrosion as tobe satisfactory in all cases excepting where the 4requirements areexcessively rigid. For the last named uses I recommend an alloy of gold60 per cent. (atomic) palladium 40 per cent. (atomic equivalent to Au.73.6 Pd. 26.4, by weight since such an allo has a hardness substantiallyequal to t at of possesses a melting point of approximately 1350 C.

w'hich is 300O more than that of gold, and will resist practically allthe corroding influences which pure platinum will withstand, and many towhich pure platinum will succumb.

As heretofore explained I do not limit myself against the use in theabove named alloys of small quantities of other noble metals,particularly such as are ordinarily found in association `withpalladium, so long as the same are used only in small amounts comparedwith the primary substances herein mentioned. It is necessary, however,that base metals be excluded.

Having thus described my invention, what I claim is l. A spark pointconsisting largely of gold and palladium whose melting point is above1150o C. and. whose hardness is at least twice that of gold.

2. An electric current communicating terminal made of an alloycomprising gold and to 40 atomic per cent. of palladium.

3. Electrical apparatus made of an alloy containing gold and ten to 40weight per cent. of palladium.

4. Apparatus of the character specified having a Working surfaceconsisting vof an alloy containing palladium and one or vmore noblemetals surrounding palladium in the periodic table, gold constituting atleast At. per cent., and palladium at least 10 At. per cent. of suchalloy.

In testimony whereof I hereunto aix my signature.

FRANK A. FAHRENWALD.

